It is very well known that useful pigments can be obtained by insolubilizing water soluble dyes. This is usually accomplished by reacting a molecularly bulky counter-ion with an acid or basic dye. For instance Lithol Rubine B, which is the azo dye of a 6-amino-m-toluene sulfonic acid and 2-hydroxy-3-naphthoic acid, is precipitated with calcium to yield Color Index Pigment Red 57. Similarly Color Index Basic Violet 10 is precipitated with phosphomolybdic or phosphotungstic acid to yield Color Index Pigment Violet 1. These dyestuffs may be permanently or non-permanently insolubilized depending on the nature of the precipitating agent. In the case of the basic or cationic dyes the complex heteropoly acids give permanent pigments while agents such as tannic acid and tartar emetic (antimony-potassium tartrate) give nonpermanent or fugitive pigments. Both of these types of pigments are used in printing inks. These organic pigments and their utility in printing inks are discussed at pages 625 to 661 of The Chemistry of Synthetic Dyes and Pigments, edited by H. A. Lubs, A.C.S. and Robert E. Krieger Publishing company, 1972. The permanent pigments from basic dyes and their uses are also discussed at pages 605 to 616 of Volume 1 of the Pigments Handbook.
It is also known to treat the surface of pigments in general to improve their dispersibility and this is extensively discussed at pages 159 to 167 of Volume 3 of the Pigments Handbook. Among these techniques is the coprecipitation of rosin with azo dyes such as Lithol Rubine B which results in a pigment with high color strengths and good transparency. A variant of this technique involves using rosin (abietic acid) derivatives with low solubility ammonium counter ions obtained from long chain aliphatic amines. Another technique involves the coating of suspended pigment particles with amines. U.S. Pat. Nos. 2,192,954 and 2,192,956 teach treating inorganic pigments with a variety of amines including quaternary ammonium salts and N-alkyl pyridinium salts such as hexadecyl trimethyl ammonium bromide and hexadecyl pyridinium bromide. Example VI of the former patent also teaches the treatment of an organic pigment, Lake Bordeaux B which is formed by the metallic salt precipitation of an anionic dye, with hexadecyl pyridinium bromide to make a printing ink.
The art also teaches the coprecipitation of a cationic surface agent and an azo pigment. These pigments precipitate upon azo coupling rather than upon complexing of cationic or anionic groups on the chromophore bearing molecule. Since these colorant compounds are water insoluble they precipitate upon formation. U.S. Pat. Nos. 3,120,508 and 3,573,946 disclose adding various ammonium salts including oleylamine-acetate, tallow fat amineacetate and coconut fat acetate to the azo coupling bath. This treatment results in an increase in the tinctorial strength. The U.S. Pat. No. 3,573,946 discloses the treatment of laked dyes as well as azo pigments. However, pigments other than those formed immediately upon azo coupling are treated well after formation of the pigment. These post treated pigments, such as copper phthalocyanines, yield printing inks with good tinctorial strength as do the inks based on the azo pigments.
There is also some suggestion in United Kingdom Patent No. 1,156,836 to treat aqueous color suspensions simultaneously with metal compounds or resins and rosin amine (dehydroabietyl amine). The precise import of this suggestion is unclear but evidently this is not intended to convey the concept of coprecipitation of a laked pigment and an amine. In the only example of a laked dye, Example 3 at page 4, the dye is first insolubilized with a barium ion and then treated with rosin amine. A similar post laking treatment is disclosed in Examples 3 and 4 at pages 4 and 5 of United Kingdom Patent No. 1,080,115 and is generically described at page 3, lines 19 to 24. However, the treating agent in this patent is a long chain aliphatic amine.
There has been interest in developing new pigments by insolubilizing dyes of good color strength. However, the inability to obtain a clean bright color on precipitation has inhibited the development of such pigments. For instance, although the pigment obtained by precipitating Color Index Basic Red 12 with silico-molybdic acid was commercially used in the United States in a very minor amount as a shading component, its color was too poor to be used as a substantial pigment component. In fact, although the Pigment and Dyestuff Manual of Bayer A.G., a producer of Color Index Basic Red 12, suggested at page 195 that a precipitate of this dye (called Astra Phloxine G) would find utility in a flexographic printing ink, it has not been so used.
This dye would be of particular interest to the printing industry if it could be converted into a clean bright pigment of good transparency. It has a shade which would make such a pigment a viable alternative to Color Index Pigment Red 81 in blends with Color Index Pigment Red 57 to yield a process red ink for the four color paper printing process. The better the quality of the process red desired, the more of the Pigment Red 81 which is used in the blend. However, the shade of the Pigment Red 81 is not ideal and it is between three and four times more expensive than the Red 57.
It has now been discovered how to obtain a pigment from Color Index Basic Red 12 which is equally clean and bluer than Color Index Pigment Red 81. It has also been discovered how to substantially improve the color value of other selected complex heteropoly acid precipitated cationic dyes.